Permittivity Enhanced Atomic Layer Deposited HfO₂ Thin Films Manipulated by a Rutile TiO₂ Interlayer

HfO 2 /TiO 2 bilayered thin films were grown on Ru and TiN electrodes at 250 °C by atomic layer deposition. The crystalline structure of the HfO 2 layer was affected by the crystalline structure of the TiO 2 under-layer. The HfO 2 layer grown on an anatase-structured TiO 2 layer crystallized into a monoclinic structure with a dielectric constant of ∼16, whereas the HfO 2 layer grown on rutile-structured TiO 2 contained a mixture of tetragonal (or cubic) and amorphous phases. This mixed structured-HfO 2 film had a higher dielectric constant of ∼29. The formation of tetragonal HfO 2 on the rutile structured TiO 2 resulted from the structural compatibility of the specific planes of the tetragonal HfO 2 and rutile structured TiO 2 . The thin HfO 2 layer with the higher dielectric constant deposited on rutile TiO 2 suppressed the leakage current effectively. Consequently, an equivalent oxide thickness of 0.41 nm from the HfO 2 /TiO 2 bilayer (thickness of HfO 2 and TiO 2 was 0.5 and 6 nm, respectively) was achieved with a leakage current of ∼2 × 10 −7 A/cm 2 at an applied voltage of 0.8 V.